Orthogonal test design to optimize the acoustic vibration method for pear texture measurement

• Vibration spectra of pears were measured by laser Doppler vibrometer (LDV) method.
• The test parameters of the LDV method were optimized.
• Optimized results were obtained based on repeatability of frequency–response curves.
• We compared the LDV method with the puncture test for pear texture measurement.
• LDV method was superior to puncture test in terms of repeatability and sensitivity.

The test parameters for pear texture measurement using a laser Doppler vibrometer (LDV) were optimized. The pear was placed in the middle of the vibration stage and excited by swept sine wave signals with a constant frequency sweeping rate and acceleration amplitude. The response signals from the tops of the pears were measured using an LDV. First, 10 pear samples were tested under different test conditions in the single-factor experiment. The test parameters included the frequency sweeping mode and rate, acceleration amplitude, pear laying style, and LDV detection point. The results show that the frequency–response curves at the same detection point have good repeatability under all tested frequency sweeping rates (regardless of the linear or logarithmic frequency sweeping mode) and acceleration amplitudes. However, the frequency–response curves at different detection points have poor repeatability for each laying style. To find a better combination of test parameters, an L27(313) orthogonal test probing the frequency sweeping rate, acceleration amplitude, pear laying style, and their 2-way interactions was designed according to the results of the single-factor experiments. No significant 2-way interaction is found among the frequency sweeping rate, acceleration amplitude, and pear laying style on the repeatability of the frequency–response curves. The test parameter values required to obtain a better repeatability are as follows: frequency sweeping rate of 23.33 Hz/s with the linear frequency sweeping mode, acceleration amplitude of 1 g (g = 9.8 m/s2), and laying style that the pear is placed with its stem upward. After the optimization of the LDV method, a total of 118 pear samples were used to compare the LDV method with the destructive puncture test. The results show that the elasticity index (EI) is well correlated with the stiffness (Stif) of pears and that the correlation is not significantly affected by the pear laying style. In addition, the LDV method is superior to the puncture test in terms of repeatability and sensitivity.